Advances in miniaturization of semiconductor devices and micro electro mechanical systems (MEMS) have increased the focus on a combination of existing photolithography and nanofabrication technology called photo imprint technology in which a resist (photocurable composition) on a wafer is shaped with a mold to form a resist pattern on the substrate. According to this technology, sub-ten-nanometer-scale fine structures can be formed on a substrate. In a photo imprint system, a resist is first applied to a pattern-forming region on a substrate and then shaped using a mold on which a pattern has been preliminarily formed. The resist is then irradiated with light to be cured and the cured product is separated from the mold. As a result, a resin pattern (photocured product) is obtained on the substrate.
In forming the resin pattern (photocured product), the thickness of the residual film of the resin pattern (photocured product) is desirably uniform across the surface of the substrate. This is to eliminate in-plane variation of line width that may result from, for example, a dry etching treatment in an etching step, which is a step other than the pattern-forming step by an imprint system in the semiconductor device fabrication process. United States Laid-open Patent Application No. 2009/0115110 teaches an imprint method of making uniform the residual film thickness of the resin pattern (photocured product). According to this imprint method, a resist is applied onto a substrate by an ink jet method and the arrangement of resist droplets is optimized in accordance with the density of the pattern to be transferred. However, according to this imprint method of arranging resist droplets in a discrete manner on a substrate, the resist droplets do not spread easily on the substrate and thus when a pattern portion formed in the mold is pressed against the resist on the substrate, bubbles tend to remain between the pattern portion and the resist. The bubbles may remain in the cured resist and the resin pattern (photocured product) may come to have an unintended shape due to the bubbles. Alternatively, a standby time may be required until the remaining bubbles disappear but this decreases productivity.
Japanese Patent No. 3700001 teaches a method for rapidly clearing the remaining bubbles. According to this method, a condensable gas that becomes condensed by capillary action generated as the resist penetrates the gaps between the substrate and the mold and recesses on the mold is introduced between the space between the mold and the substrate so that the condensable gas becomes condensed, resulting in volume reduction. The condensable gas employed in Japanese Patent No. 3700001 is trichlorofluoromethane (CFCl3). Japanese Journal of Applied Physics, Vol. 47, No. 6, 2008, pp. 5151-5155 teaches that a filling property can be improved by employing 1,1,1,3,3-pentafluoropropane (CHF2CH2CF3) as the condensable gas.
However, even in such processes that use condensable gases, the force (mold releasing force) required to separate (release) the mold from the resist cured film has been large.